1. Field of the Invention
The present invention relates to an imaging apparatus and an image processing method and, in particular, to technologies for speedily and accurately calculating a white balance gain.
2. Description of the Related Art
Japanese Patent Application Laid-Open No. 2007-295300 (hereinafter referred to as PTL 1) discloses an imaging apparatus that calculates a white balance gain (WB gain) on the basis of an image thinned (extracted) from an image in the entire region of an image pickup device, actually takes an image in a part of the image pickup device through electronic zooming, and performs white balance correction with the calculated WB gain. Accordingly, a color temperature is detected from an image in a region having a higher probability that white exists than a region where an image is to be actually taken, thereby allowing a WB gain to be accurately calculated.
Japanese Patent Application Laid-Open No. 2003-116143 (hereinafter referred to as PTL 2) includes description where signals of pixels are thinning-read from a solid image pickup device, or signals of multiple pixels on lines with the same color in the vertical direction are added together and read, and a WB gain is calculated by detecting (an integration process of the level of each color) the read signals.
Incidentally, an image pickup device adopted in each of the imaging apparatuses described in the foregoing PTLs 1 and 2 has a color filter array that is a Bayer array (paragraph [0023] and FIG. 4 in PTL 1, and FIG. 3 in PTL 2).
In the Bayer array, green (G) pixels are arranged checkerwise and red (R) and blue (B) are line-sequentially arranged. Accordingly, there is a problem in that aliasing of a high frequency signal exceeding a reproduction band for each color and deviation in phase of each color cause coloring (color moire) at low frequencies.
In order to solve such a problem, a color image pickup device has been proposed that has a three-color random array satisfying an array limitation condition where any pixel concerned is adjacent to three colors including the color of the pixel concerned on any of four sides of the pixel concerned (Japanese Patent Application Laid-Open No. 2000-308080; PTL 3).
Japanese Patent Application Laid-Open No. 8-23542 (hereinafter referred to as PTL 4) proposes an imaging apparatus that includes G filters having a higher ratio than R filters and B filters to increase the color resolution in the horizontal direction and the vertical direction and reduce color moire in a luminance signal in comparison with the case where color filters with the same ratio are arranged in a lattice structure.